Best Stitch for a Warm Blanket

[Eri]

I am a novice crocheter and I want to make blankets for people who can’t afford them this winter. What’s a good stitch that would make a very warm blanket even if used outside or without heating? And what type of yarn would be best?

[Granny Square]

I would guess the warmest would be either SC or HDC (US terms)  There is a stitch called the thermal stitch, which is probably more meant for potholders, that is extremely dense and stiff and would use the most yarn of those 3.  Here is one tutorial,

You are probably going to get different opinions, I'd opt for acrylic.  I have made (mostly knit)  a lot of winter pullover sweaters in acrylic and they are plenty warm (am wearing one now), but I'm not sitting outside in the snow, either.  I don't use a lot of wool, but wool is probably going to cost at least 2x more than acrylic, so if your goal is to make several blankets without breaking the bank, it's probably the way to go to get the most people warm. 

[bgs]

I agree with Granny Square.  Sc and hdc make a denser fabric so should be warmer.  I also agree with what she said about wool and acrylic.  I hear wool is warmer and is supposedly still warm even if wet so its supposedly good if you are out in weather.  Some people like me are allergic to wool. 

[Granny Square]

Huh!  Interesting about wool, I just remembered hating the wool sweaters that itched like heck when I was a kid.  I've knit a lot of wool/nylon socks in the last few years (since moving from California to Oregon - brr!), and they don't itch so my old kid sweaters probably were just cheap wool.

https://adventure.howstuffworks.com/outdoor-activities/hiking/wool-when-wet.htm